This invention relates generally to devices that measure the orientation of bodies and more specifically to devices that measure the orientation of rotating bodies that are used in measuring acceleration.
The accelerometers used in inertial navigation systems are typically of the pendulous torque-to-balance variety. A typical unit uses a hinged pendulum as the acceleration sensing body. An orientation sensor produces an error signal when the pendulum begins to pivot away from its desired null position as a result of an acceleration, and this error signal is used by a control circuit to maintain the pendulum in its null position by means of an electrical control signal applied to a torquing device. The magnitude of the electrical control signal is proportional to the acceleration and thus is a measure of the acceleration.
The centripetal opposed pendulous accelerometer (COPA) described herein offers a new approach to the design of precision accelerometers in that it utilizes a spinning body as the acceleration sensing element. The sensing element spins in a dry environment, and there are consequently no fluid migration/stratification/compatibility issues which might argue against a long operating life. No electrical connections to the sensing element are required, and the device is radiation hard.
The operation of a COPA entails measuring the tilt of the sensing element with an orientation sensor. The preferred orientation sensor is one which measures the tilt of the sensing element by the deflection of a beam of light reflected from a surface of the sensing element. A precise measurement of tilt can be achieved only if the intensity of the light is precisely regulated.